Too-tall form with its head in the clouds (plural, not "The Cloud")

I have this code to center a form on the screen:

Java Code:

frame.setLocationRelativeTo(null);

It works fine on my dev machine (XP), but on another (W2K), the top of the form is up out of sight, and I cannot reach the title bar to move it down or the close button to close it (Alt+F4 works, of course).

I installed the same runnable jar file on another machine and, when I tried to run it, got "Could not find the main class"

What the deuce? These are all Windows machines; on one (the dev machine) it runs fine, on another it runs but also runs out of real estate, and on the third one it doesn't run at all. It reminds me of the problem Yogi Berra had with his catchers when he was managing the Yankees.